Exudation of plasma and production of thromboxane in human bronchi after local bradykinin challenge

Heteromerization fingerprints between bradykinin B2 and thromboxane TP receptors in native cells

Bradykinin (BK) and thromboxane-A2 (TX-A2) are two vasoactive mediators that modulate vascular tone and inflammation via binding to their cognate "class A" G-protein coupled receptors (GPCRs), BK-B2 receptors (B2R) and TX-prostanoid receptors (TP), respectively. Both BK and TX-A2 lead to ERK1/2-mediated vascular smooth muscle cell (VSMC) proliferation and/or hypertrophy. While each of B2R and TP could form functional dimers with various GPCRs, the likelihood that B2R-TP heteromerization could contribute to their co-regulation has never been investigated. The main objective of this study was to investigate the mode of B2R and TP interaction in VSMC, and its possible impact on downstream signaling. Our findings revealed synergistically activated ERK1/2 following co-stimulation of rat VSMC with a subthreshold dose of BK and effective doses of the TP stable agonist, IBOP, possibly involving biased agonist signaling. Single detection of each of B2R and TP in VSMC, using in-situ proximity ligation assay (PLA), provided evidence of the constitutive expression of nuclear and extranuclear B2R and TP. Moreover, inspection of B2R-TP PLA signals in VSMC revealed agonist-modulated nuclear and extranuclear proximity between B2R and TP, whose quantification varied substantially following single versus dual agonist stimulations. B2R-TP interaction was further verified by the findings of co-immunoprecipitation (co-IP) analysis of VSMC lysates. To our knowledge, this is the first study that provides evidence supporting the existence of B2R-TP heteromerization fingerprints in primary cultured VSMC.

Pharmacology of Bradykinin-Evoked Coughing in Guinea Pigs

Bradykinin has been implicated as a mediator of the acute pathophysiological and inflammatory consequences of respiratory tract infections and in exacerbations of chronic diseases such as asthma. Bradykinin may also be a trigger for the coughing associated with these and other conditions. We have thus set out to evaluate the pharmacology of bradykinin-evoked coughing in guinea pigs. When inhaled, bradykinin induced paroxysmal coughing that was abolished by the bradykinin B2 receptor antagonist HOE 140. These cough responses rapidly desensitized, consistent with reports of B2 receptor desensitization. Bradykinin-evoked cough was potentiated by inhibition of both neutral endopeptidase and angiotensin-converting enzyme (with thiorphan and captopril, respectively), but was largely unaffected by muscarinic or thromboxane receptor blockade (atropine and ICI 192605), cyclooxygenase, or nitric oxide synthase inhibition (meclofenamic acid and N(G)-nitro-L-arginine). Calcium influx studies in bronchopulmonary vagal afferent neurons dissociated from vagal sensory ganglia indicated that the tachykinin-containing C-fibers arising from the jugular ganglia mediate bradykinin-evoked coughing. Also implicating the jugular C-fibers was the observation that simultaneous blockade of neurokinin2 (NK2; SR48968) and NK3 (SR142801 or SB223412) receptors nearly abolished the bradykinin-evoked cough responses. The data suggest that bradykinin induces coughing in guinea pigs by activating B2 receptors on bronchopulmonary C-fibers. We speculate that therapeutics targeting the actions of bradykinin may prove useful in the treatment of cough.

Bradykinin induces vascular contraction after hemorrhagic shock in rats

BACKGROUND

Bradykinin (BK) has many biological effects in inflammation, allergy, and septic shock. Studies have shown that low doses of BK can induce vascular relaxation and high doses can induce vascular contraction in many pathophysiological conditions, but the role and mechanisms that high doses of BK have on vascular contraction in hemorrhagic shock are not clear.

METHODS

With hemorrhagic-shock rats and hypoxia-treated superior mesenteric artery (SMA), we investigated the role and mechanisms of high doses of BK-induced vascular contraction in hemorrhagic shock.

RESULTS

High doses of BK (500-50,000 ng/kg in vivo or 10(-10) to 10(-5) mol/L in vitro) dose dependently induced vascular contraction of SMA and increased the vascular calcium sensitivity in normal and hemorrhagic-shock rats. Less than 10(-10) mol/L of BK induced vascular dilation BK-induced increase of vascular contractile response and calcium sensitivity was reduced by denudation of the endothelium, 18α-glycyrrhetic acid (an inhibitor of myoendothelial gap junction) and connexin 43 antisense oligodeoxynucleotide. Further studies found that high concentrations of BK-induced vascular contraction in hemorrhagic shock was closely related to the activation of Rho A-Rho kinase pathway and Protein Kinase C (PKC) α and ε.

CONCLUSIONS

High doses of BK can induce vascular contraction in hemorrhagic shock condition, which is endothelium and myoendothelial gap junction dependent. Cx43-mediated activation of Rho A-Rho kinase and Protein Kinase C (PKC) pathway plays a very important role in this process. This finding provided a new angle of view to the biological role of BK in other pathophysiological conditions such as hemorrhagic shock or hypoxia.

New topics in bradykinin research

Bradykinin has been implicated to contribute to allergic inflammation and the pathogenesis of allergic conditions. It binds to endothelial B(1) and B(2) receptors and exerts potent pharmacological and physiological effects, notably, decreased blood pressure, increased vascular permeability and the promotion of classical symptoms of inflammation such as vasodilation, hyperthermia, oedema and pain. Towards potential clinical benefit, bradykinin has also been shown to exert potent antithrombogenic, antiproliferative and antifibrogenic effects. The development of pharmacologically active substances, such as bradykinin receptor blockers, opens up new therapeutic options that require further research into bradykinin. This review presents current understanding surrounding the role of bradykinin in nonallergic angioedema and other conditions seen by allergists and emergency physicians, and its potential role as a therapeutic target.